1. Field of the Invention
The present invention relates to a constant current source apparatus for supplying a constant current to at least one load.
2. Description of the Related Art
A prior art constant current source apparatus is constructed by a gate-source short-circuited depletion-type metal oxide semiconductor (MOS) transistor connected between a load connected to a power supply terminal and a ground terminal, so that a load current flowing through the load is made constant (see: FIG. 5 of JP-5-13686-A). This will be explained later in detail.
In the above-described prior art constant current source apparatus, however, when a voltage applied thereto fluctuates, the load current would fluctuate due to the channel length modulation effect of the depletion-type MOS transistor.
Also, in the above-described prior art constant current source apparatus, where the voltage applied thereto is too high, no use is made of a low drain-to-source breakdown depletion-type MOS transistor, which would increase the layout area and degrade the current characteristics.